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IC 


8983 



Bureau of Mines Information Circular/1984 



Improved Personnel Access 
for Surface Mining Equipment 



By Dennis A. Long 




UNITED STATES DEPARTMENT OF THE INTERIOR 



Information Circular 8983 



Improved Personnel Access 
for Surface Mining Equipment 



By Dennis A. Long 




UNITED STATES DEPARTMENT OF THE INTERIOR 
William P. Clark, Secretary 

BUREAU OF MINES 
Robert C. Horton, Director 







Library of Congress Cataloging in Publication Data: 



Long, Dennis A 

Improved personnel access for surface mining equipment. 

(Information circular / U.S. Dept, of the Interior, Bureau of Mines ; 
8983) 

Bibliography: p. 19. 

Supt. of Docs, no.: I 28. 27:8985. 

1. Strip mining— Equipment and supplies— Safety measures. 2. 
Ladders— Safety measures. 3. Stairs— Safety measures. I. Title. II. 
Series: Information circular (United States. Bureau of Mines) ; 8983. 



TN295,U4 [TN291] 622s [622'.8] 84=600089 






\J 



CONTENTS 



<^ Page 

k 

1^ Abstract 1 

N. Introduction 2 

(>^ Safety hazard assessment 2 

"^ Haulage trucks and front-end loaders 3 

Access design problems 3 

Improved ladders 7 

Development 7 

Description and use 12 

Track dozers and shovels 13 

Access design problems 13 

Powered safety steps 14 

Development 14 

Description and use 16 

Summary and economic considerations 18 

References 19 

Appendix 20 

ILLUSTRATIONS 

1. Typical ladder on off -highway haulage truck 3 

2. Ladder located at right front of truck 4 

3 . Truck bumper as part of ladder system 5 

4. Damaged truck ladder 6 

5 . Cable ladder showing height of first step 8 

6. Cable ladder showing lack of rigidity when stepped on 9 

7 . Pre-tensioned spring step design 10 

8. Spring step retrofitted to truck ladder 11 

9 . Spring step during collision 12 

10. Track dozer 14 

11. Loading shovel 15 

12. Powered safety step on loading shovel 16 

13. Powered safety step on track dozer 17 

TABLES 

1. Recommended design dimensions for ladder systems on large haulage trucks 

and front-end loaders 7 

2 . Pre-tensioned spring specifications 10 

A-1 . Field test locations for pre-tensioned spring step 20 

A-2. Equipment used for evaluating pre-tensioned spring step 20 

v^ A-3. Field test locations for powered safety step 20 

1 A-4. Equipment used for evaluating powered safety step 20 

^-a 

'^ 



UNIT OF MEASURE 


ABBREVIATIONS 


USED IN 


THIS REPORT 


deg degree 




lb 


pound 


ft foot 




pet 


percent 


in inch 




yr 


year 



IMPROVED PERSONNEL ACCESS FOR SURFACE MINING EQUIPMENT 

By Dennis A. Long 



ABSTRACT 

Slip and fall accidents are a major cause of lost-time injuries asso- 
ciated with large mobile equipment in surface mines. An evaluation of 
the safety hazards associated with getting on and off large surface 
mining vehicles showed that most of the accidents occur at the point 
where personnel attempt to mount or dismount the machine at ground lev- 
el. The major hazardous design conditions were identified as exces- 
sively flexible supports for lower steps or rungs, inappropriate 
ground-level-to-first-step distances, poor step designs, access designs 
that use vehicle components as steps or walkways, and inadequate hand- 
rail and guardrail designs. Additional hazards are introduced by the 
lack of proper maintenance of ladder hardware and the work practices of 
operators in carrying articles while mounting and dismounting the vehi- 
cle. This Bureau of Mines report describes the design and in-mine 
testing of improved access systems for large mobile mining equipment. 



^Mining engineer. Twin Cities Research Center, Bureau of Mines, Minneapolis, MN, 



INTRODUCTION 



Mobile equipment manufacturers and min- 
ing companies recognize the difficulty of 
getting on and off the large mining 
equipment. Overall, there is a lack of 
effective guidance and design standards, 
and access systems appear to have been 
added as an afterthought in mobile equip- 
ment design. Thus, the stringent system 
design concepts employed for most of the 
machine features are not generally ap- 
plied in ladder access designs. 

On-site reviews were conducted to iden- 
tify design deficiencies of access lad- 
ders being used in surface mines. These 
reviews focused on handrail specifi- 
cations, step and ladder design, step 
and ladder placement, ground clearance, 
environment-induced problems , and human 
factors. General design problems were 
identified along with numerous specific 
safety problems. 

Design diversity and lack, of good safe- 
ty analysis may be a direct cause of the 
high slip and fall rates associated with 
mobile mining equipment. For example, 
drivers and maintenance personnel must 
usually work with various types of vehi- 
cles, creating a "transfer of training" 
problem associated with ladders of dif- 
ferent designs. In moments of inatten- 
tion or carelessness, or in emergencies, 
people react according to how they "ex- 
pect" to find access hardware. When de- 
signs deviate from these expectations 
(e.g., a step is only half as wide as the 
one above or below it), the potential for 
accidents increases. 

A review of a large number of mine mo- 
bile equipment (J^)^ identified the fol- 
lowing significant design deficiencies: 

• Inadequate handrail and guard- 
rail designs, which increase the 



difficulty of mounting and dismounting 
the vehicle. 

• Excessively flexible lower section 
supports for lower steps or rungs on lad- 
ders, making ascent or descent difficult. 

• Inappropriate ground-level-to-first- 
step distances, which create hazards. 

• Poor step designs that permit accu- 
mulations of mud, snow, ice, grease, and 
oil and create hazardous footing. 

• Access paths that require use of 
equipment components as primary steps , 
such as the tracks on dozers and shovels. 

• Work practices of operators in car- 
rying personal articles on and off the 
equipment introduce additional hazards. 

The access problem involves two types 
of mobile equipment. The first category 
includes haulage trucks and front-end 
loaders. These vehicles have vertical or 
near vertical ladders in the vicinity of 
the cab. Analysis has shown that the 
chief hazards are found in the first few 
steps of the ladder where the operator 
mounts or dismounts the machine (2^) . The 
second category includes tracked vehi- 
cles, such as dozers, shovels, and drag- 
lines. These vehicles have one common 
hazard: the primary access path usually 
involves using the track as a step, walk- 
way, or both. 

The Bureau conducted this investigation 
to determine and reduce the hazards asso- 
ciated with mounting and dismounting 
large mine mobile equipment. This report 
summarizes the research results for each 
of the two types of equipment , and in- 
cludes recommendations for alleviating 
the access problem. 



SAFETY HAZARD ASSESSMENT 



Evaluation of the safety hazards asso- 
ciated with mobile equipment in surface 

^Underlined numbers in parentheses re- 
fer to items in the list of references 
preceding the appendix. 



mines confirmed that slip and fall acci- 
dents account for a substantial propor- 
tion of vehicle related accidents. Ac- 
cording to 1978-79 data from the Mine 
Safety and Health Administration (MSHA) , 
U.S. Department of Labor, slips and falls 



while mounting and dismounting machines 
constitute over one-third of all lost- 
time accidents associated with the opera- 
tion of haulage trucks, front-end load- 
ers, track dozers, shovels, and draglines 
(2^) . These five types of equipment ac- 
count for 80 pet of the mobile equipment 
operating in U.S. surface mines. An 
average slip and fall results in 15.3 
lost worker days and the characteristic 
injuries resulting from getting on and 
off mobile equipment are cuts, lacera- 
tions, contusions, fractures, sprains, 
and strains. The hands, fingers, back, 
legs, and feet are most frequently in- 
jured in these accidents (2). 



The slip and fall accident reports were 
further analyzed to determine where in 
the process of mounting or dismounting 
the machine people are getting hurt. The 
analysis revealed that 40 pet of all sur- 
face mine equipment slip and fall acci- 
dents occurred at the first step on the 
vehicle; that is, during the operator's 
initial attempt to mount or dismount the 
vehicle, with the accident occurring at 
the zone between the equipment and the 
ground (2^) . Nearly 60 pet of all slip 
and fall accidents involving track dozers 
occur at this point. 



HAULAGE TRUCKS AND FRONT-END LOADERS 



ACCESS DESIGN PROBLEMS 

Off -highway haulage trucks usually have 
ladders mounted on the front of the truck 



adjacent to the left side of the engine 
compartment (figs. 1-2), with the angle 
of inclination between 75° to 90° (verti- 
cal) . On some model trucks, the bumper 







FIGURE 1. - Typical ladder on off-highway haulage truck. 




FIGURE 2. - Ladder located at right front of truck. 



is used as part of the ladder structure 
(fig. 3). Most of the designs have lower ^ 
steps supported by flexible material such 
as wire rope, chain, or a rubber belting 
material. 

The ladders used on almost all front- 
end loaders are located directly along- 
side the cab. This design forces the 
operator to change direction in the mid- 
dle of the ladder in order to open the 
door. He must also negotiate a difficult 
transition from the ladder into the cab. 
Some front-end loaders have a movable or 
retractable ladder that the operator must 
pull down to mount the vehicle. 

Ladders provided as original equipment 
are often easily damaged once the vehicle 



operates in the mine environment, and 
even slight damage can render them in- 
operable. A damaged ladder represents a 
safety hazard (fig. 4). In many cases, 
after making numerous repairs, the mine 
maintenance shop personnel will construct 
a ladder from available scrap steel, ca- 
ble, and grip-strut material. Conse- 
quently, a wide range of ladder designs 
exists throughout the mining industry. 
Ladder reliability is directly related to 
the complexity, placement, and quality of 
installation. 

The most significant problem or defi- 
ciency of the primary ladder system is 
the lower steps. Within the open pit 
mine environment , the problem of vehicle 
ground clearance is critical; the truck 




FIGURE 3. - Truck bumper as part of ladder syste 



m. 




FIGURE 4. - Damaged truck ladder. 



is designed to ensure the maximum possi- 
ble ground clearance. The lower portion 
of the primary ladder assembly must be 
below this level for the operator to 
reach the first step, placing the first 
two steps in a vulnerable position. As a 
result, the ladders are subjected to con- 
tinual impacts from the objects in the 
roadway. 

To minimize damage, lower ladder sup- 
ports are usually constructed from a very 
flexible material. Usually this means 
suspending the lower one or two steps on 
a cable which is then mounted to the 
bumper or the ladder. These wire rope or 
cable ladders are invariably knocked out 
of position, and do not return to their 
initial configuration (figs. 5-6). The 
height of the lower rung is usually about 
36 to 42 in above the ground. Drivers 
and other personnel ascending or de- 
scending the vehicle using these damaged 
lower steps are subject to knee and shin 
bruises, scrapes, or worse. The flexi- 
bility of the ladder supports for the 
lower steps and the fact that the steps 
are too high for the operator to mount 
and dismount the machine safely contrib- 
utes to the slip and fall accidents. 



IMPROVED LADDERS 

Development 

In 1978, the Bureau of Mines began to 
design and develop improved ladder de- 
signs for haulage trucks and loaders. 
Several alternative designs were sub- 
jected to human-factor field evaluation 
and structural testing demonstrations in 
various surface mines. The effort was 
first focused on off-highway haulage 
trucks, and design recommendations were 
developed for improved total access sys- 
tems. Table 1 summarizes the recommended 
ladder dimension systems for large haul- 
age trucks and loaders (_3) . Field inves- 
tigations showed that the most serious 
design deficiencies were at the lower end 
of the ladders; further Bureau of Mines 
research focused on solving the problem 
of the lower ladder design. 

Several primary lower ladder designs 
were subjected to use by mine personnel 
and field evaluation, and structural- 
testing demonstrations. As a result of 
the initial field demonstrations, it was 
concluded that the four-spring design 
(figs. 7-8) could appreciably reduce slip 



TABLE 1. - Recommended design dimensions for ladder systems 
on large haulage trucks and front-end loaders (3) 



Parameter 



Specification 



Minimum Maximum 



Angle of inclination deg. . 

Step dimensions, in: 

First-step height above ground 

Distance between steps ^ 

Distance from top step to platform 

Ladder depth^ 

Step width 

Step depth^ 

Handrail dimensions, in: 

Diameter 

Height above ground 

Width between at ground level 

Hand clearance 

Height above landing 



76 



90 



None 


28 


10 


12 


10 


12 


8 


10 


12 


16 


4-3/4 


7-1/2 


3/4 


1-1/2 


28 


56 


18 


21 


3 


None 


33 


36 



'Measured vertically from top of step to top of step. 
^To provide a minimum of 3 in from back of step to pan for 
toe clearance and a passage for debris to drop through. 
^Standard dimensions for grip-strut step material. 




FIGURE 5. - Cable ladder showing height of first step. 




FIGURE 6. - Cable ladder showing lack of rigidity when stepped on. 



and fall accidents on haulage trucks 
and loaders. The first-generation spring 
steps were evaluated for operator accept- 
ability and structural performance at the 
Cyprus Pima Mine, south of Tucson, AZ, 
in 1978, and at the Bingham Canyon Mine, 
near Salt Lake City, UT, in 1979 ( 4_) . 

The prototype lower steps substantially 
reduced the height of the first step and 
were much more rigid when stepped on, or 
off. Because of their high stiffness co- 
efficient and the pre- tensioning of the 
springs, the prototype lower steps close- 
ly maintained the step distance and the 
angular inclination of the ladder. How- 
ever, the pre-tensioned springs used in 
the first step proved to be too brittle 
to withstand the rugged mine environment. 



placement of the spring step on the mine 
vehicle. For example, a step mounted 
either directly on the bumper or on the 
side of the vehicle is likely to have 
limited survivability. 

As a result of the in-mine test- 
ing, a second-generation pre-tensioned 
spring step was developed. The second- 
generation design parameters are listed 
in table 2. The most significant change 
was to adopt a modular design; rather 
than a one-piece welded unit, the grip- 
strut steps and each two-spring set are 
replaceable as individual parts. Further 
development has made the pre-tensioned 
springs more durable, using more rigid 
spring steel and different welding 
techniques. 



The test program demonstrated that 
proper installation techniques were im- 
portant for the survivability of the 
spring step. These techniques include 
good welding practices and proper 



A followup testing program was con- 
ducted at seven surface mines , where 
various types of haulage trucks larger 
than 100-ton capacity were fitted with 
ladders of the new design (2). The 



10 



TABLE 2. - Pre-tensioned spring specifications 



Material , 

Rockwell hardness 

Spring, OD in, 

Wire size in. 

Type of ends , 

Direction of helix , 

Pre-tension lb. 

Free length in, 



Chrome-nickel steel, 17-7 pH 

(ASTM 3-313 or AMS 5678) 
47-52, C-scale 
1.75+0.030 
0.312 

Ground, plain 
LH, optional 
150±10 
11-1/8 



NOTE. — Tensile test coupons 8 in long should be taken of 
wire before winding each spring lot and also of each heat 
lot and shipped with springs for quality control. 



ladders were subjected to normal operat- 
ing use for at least 1 yr, during which 
evaluations were made of the safety, 
maintenance, and driver acceptance of the 
spring step. Further field testing of 
the pre-tensioned spring step is being 
conducted at six additional mines using a 



variety of mobile equipment. The mines 
and equipment are listed in the appendix 
tables. Table A-1 identifies the mines 
where the spring step has been field 
tested, and table A-2 lists the surface 
mining equipment on which spring steps 
have been installed. 



FOUfi SFRINe-SDPPORTED LOWER STEPS 



RIGID LADDER 
ASSEMBLY 




GRIP-STRUT 
STEP MATERIAL 



PRE-TENSION SPRING 
ASSEMBLY 



FIGURE 7. - Pre-tensioned spring step design. 



11 








FIGURE 8. - Spring step retrofitted to truck ladder. 



Since 1978, about 30 spring steps were 
field tested at 13 mines on 27 vehicles. 
The results of the field testing indicate 
that the pre-tensioned spring step can 
help prevent first-step accidents. How- 
ever, the testing also shows that proper 
installation techniques, correct vehicle 
applications , and management support for 
proper maintenance are important for long 
life of the spring step. Spring-step 
failure occurred for a variety of rea- 
sons, and the damage inflicted on the 
spring ladders varied greatly from mine 
to mine. At some mines, the ladders sus- 
tained damage after 3 or 4 weeks; at oth- 
ers, ladders remained on the trucks with 
little or no damage for more than a year. 
The most common reasons for failure 
included shear at the point where the 
step is welded to the ladder, spring 
failure resulting from low ground clear- 
ance, and lack of operator or supervisory 
acceptance. Some damage seemed to be a 



result of a misconception that the Bureau 
of Mines spring step is indestructible. 
In several cases , the vehicle operator 
may have been experimenting to see how 
much punishment the spring step could 
withstand. 

In summary, the following include the 
results from the long-term field tests. 
These points should be considered in all 
future spring step applications: 

1 . The ladders should be mounted 
higher than they were in most of the test 
installations. The spring failures oc- 
curred mostly at the connection of the 
upper supporting springs and the collar. 
By mounting it higher, this connection 
would be more protected. Although Soci- 
ety of Automotive Engineers (SAE) stan- 
dards advise a 28-in minimum ground 
clearance, best results will occur at 
heights greater than 30 in. In mines 



12 



that have parking ditches or extraordi- 
nary ground clearance problems (soft, 
muddy haulroads or special guide berms), 
the operator should ensure that the bot- 
tom of the step will not undergo continu- 
ous ground impact. 

2. Never install the spring step di- 
rectly on the bumper. This causes large 
shear forces to develop at the top of the 
step. 

3. Proper welding and installation 
techniques are important. Normally, in- 
stallation will take around 2 worker 
hours, and should be supervised. 

4. The spring step should only be in- 
stalled perpendicular to primary vehicle 
movement; e.g., never install the spring 
step on the side of a haulage truck. 



5. Vfliere possible, the complete three- 
step unit (as shown in figure 7) should 
be used, even if part of the existing 
ladder must be cut off to maintain suffi- 
cient ground clearance. 

6. Keep the step weight as low as pos- 
sible by using lighter gauge metal. 

7. Spring step width should correspond 
to the overall ladder width; and a 15-in 
step width for front-end loaders and 
rubber-tired dozers. 

Description and Use 

The spring ladder concept is shown 
in figure 9. The design is to provide 
the operator with basic human-factor de- 
sign and to minimize damage to the lower 
steps on the primary ladder system. The 




FIGURE 9. = Spring step during collision. 



13 



ladders are designed to deflect with min- 
imal damage when impacting an object, but 
support the weight of the operator with 
minimal deflection (less than 2 in). 

The steps are highly resistent to col- 
lision damage because they yield on im- 
pact if rammed into obstructions such as 
rocks or berms. The ground clearance re- 
quired for rigid ladders mounted on large 
mining equipment is commonly 36 to 42 in. 
The flexibility of the durable spring- 
mounted supports allows the new ladders 
to be mounted with the bottom step be- 
tween 24 and 36 in above the ground, de- 
pending on the application. 

The spring step is a totally passive 
system; i.e., it needs no activation by 
the operator. The unit consists of two 
steps constructed with grip-strut mate- 
rial to minimize the acciimulation of de- 
bris and provide an antiskid surface for 
good footing. The steps are joined with 
two pairs of spring assemblies and mount- 
ing brackets. The mounting brackets con- 
sist of a flat plate and a collar to sup- 
port the spring, which is welded to the 
flat plate. The springs are fabricated 



from stainless steel and pre-tensioned to 
150 lb. The best results will be ob- 
tained by following the specifications 
developed in Bureau of Mines contract 
(2^). The entire primary ladder assembly, 
including the spring ladder, should con- 
form to the SAE requirements (3) . These 
SAE recommendations cover access sys- 
tems for large construction and mining 
machines, and specify ladder inclination, 
handrail dimensions and clearance, rung 
spacing, rung width, and other features. 

There are other options available for 
using the spring step. On some trucks, a 
single-step spring ladder was installed 
in place of the standard oil check step. 
These ladders underwent no damage dur- 
ing the course of the program, but these 
steps were in a more protected area 
mounted under the engine compartment. On 
certain front-end loaders and smaller 
haluage trucks, a single-step ladder 
(one-half of ladder shown in figure 7) 
was installed at the bottom of the lad- 
der. However, wherever possible, the 
double spring step should be used for op- 
timum survivability. 



TRACK DOZERS AND SHOVELS 



ACCESS DESIGN PROBLEMS 

Over the past decade, the size of track 
dozers in surface mines has increased 
substantially. Today the operator must 
climb 4 ft or more to mount the dozer, 
usually stepping onto or climbing over 
the track assembly. Because of the harsh 
working environment encountered by the 
dozer, the tracks are usually covered by 
mud, snow, or ice, making them an unsat- 
isfactory accessway. 

On some dozers, the track assembly is 
the only way to mount the vehicle (fig. 
10). In this situation, the operator 
must use the track grips to mount the 
dozer at the rear of the machine, then 
walk on the track to reach the cab. On 
certain large dozers, the person must 
mount the machine at the front by step- 
ping onto the blade arm and then walking 
along the track to enter the cab. On 



some machines , the person uses a toe-hole 
in the side track frame, then steps up to 
the track. In any event, the distance 
from the ground to the track usually ex- 
ceeds 48 in, presenting a challange under 
any environmental condition. 

The ladders and stair systems used on 
mining shovels and draglines vary in 
quality of design and safety. Many of 
the larger excavators use electricity 
or hydraulically operated stairways for 
access to the main decking or cab. Small 
to medium machines often utilize sev- 
eral variations of the pull-down and 
counterbalanced-stair systems (fig. 11). 

The Bureau's work determined that the 
design area requiring the most work was 
the zone where the operator mounts or 
dismounts the piece of equipment. Almost 
all models require the operator to climb 
over the track assembly. An improved 



14 




FIGURE 10. - Track dozer. 



system would result in a safer method of 
transporting operators and materials up 
and over the track assembly. 

There have been several efforts to de- 
vise alternative entry systems for track 
dozers and shovels. One method used a* 
ladder extending out over the tracks. A 
second method entailed the use of a load- 
ing berm that the dozer pulled up next 
to, permitting the operator to exit via 
the berm, rather than having to climb 
down the tracks. A third method, spon- 
sored by the Bureau of Mines on a cost- 
sharing basis , uses a hydraulic lift 
"power step" to transport the person from 
the ground level to the cab. This devel- 
opment has proved to be a practicable 
solution to the access problem on track 
dozers and shovels. 



POWERED SAFETY STEP 

Development 

The powered safety step was designed in 
1975. A prototype unit was installed on 
a Caterpillar 16G grader at Consolidation 
Coal Co.'s Glenharold Mine, near Stanton, 
ND, This unit is still in operation 
after 7 yr of continuous service. In 
view of its potential to reduce the num- 
ber of accidents caused by slips and 
falls from large mining equipment, in 
1978 the Bureau of Mines began working 
with the powered step on a cost-sharing 
basis to make the technology more mine- 
worthy. This work included developing 
and fabricating step-design alternatives, 
and conducting in-mine tests to determine 



15 




FIGURE 11. - Loading shovel. 



survivability of the 
mine environment. 



step in the rugged 



Since 1978, the powered step has been 
field tested at different mines in North 
Dakota, Indiana, Illinois, Wyoming, and 
Tennessee. Thirty of the test units are 
still in operation and many more have 
been sold commercially during the past 2 
yr. Current installations of the powered 
step include loading shovels, track doz- 
ers , draglines , haulage trucks , and 
graders. Table A-3 lists the field test 
locations, and table A-4 lists the mining 
equipment on which the powered steps have 
been installed. 

The results of the field testing have 
proved conclusively that the powered 
safety step can solve the problem of 
mounting and dismounting tracked mining 
vehicles. Almost 90 pet of the powered 
step units are still in use today on the 



original machines; several step units 
have been in continual use for more than 
5 yr. The mines have reported that main- 
tenance is surprisingly low and survival 
is high. 

Almost without fail, installations on 
shovels , draglines , and dozers have 
proved successful over the long-term. 
More recently, installations on haulage 
trucks , graders , and scrapers have shown 
promising results. The following com- 
ments were made by the mine personnel in- 
volved with the field testing of the pow- 
ered steps: 

• "The safety steps that we have on 
our equipment are well accepted by em- 
ployees and management . " 

• "We feel that slip and fall acci- 
dents have been virtually zero since we 
installed these steps. They have been 



16 



accepted by the mining crews , and they 
would not be without them," 

• "It is the best method for getting 
on and off large shovels that I have ever 
seen. We plan to install similar appara- 
tus on all our shovels. We have not had 
any accidents with the powered steps. 
Very well accepted by all employees." 

• "I have been associated with these 
powered steps from the very beginning. 
We have had very few maintenance problems 
with the step." 

Description and Use 

The powered safety step is a hydrauli- 
cally powered device to lift personnel 
and materials from the ground to working 
levels on large equipment (figs. 12-13). 
The primary application of the powered 
step is for the large track dozers, 
shovels, and draglines. It eliminates 



hazardous blind steps, and makes it un- 
necessary for the operator to climb on 
irregular surfaces such as the track or 
push arm (_5) . 

The step is activated by a self- 
contained electric-hydraulic unit. Power 
comes either from the vehicle's auxiliary 
power supply or from its own battery 
source, depending on the application. 
When the step is in the "down" position, 
it rests approximately 15 in from ground 
level. When the machine is operating, 
the step automatically locks in the "up" 
position, protecting it against damaging 
obstructions. Visual alarms and machine 
interlocks are provided where necessary 
to prevent machine operation when the 
step is in the "down" position. On ro- 
tating machines, such as draglines and 
shovels, an electrical interlock is pro- 
vided to prevent operation of the swing 
motors when the step is down (5). 




4r '■w^l! 

FIGURE 12. - Powered safety step on loading shovel 



17 




FIGURE 13. - Powered safety step on track dozer. 



18 



During step operation, when the power 
unit is activated with an electrical 
switch located on the step, a single cy- 
linder attached between two lifting arms 
smoothly lifts the step. The step is 
lowered by activating a pressure-release 
solenoid, bypassing the hydraulic pump. 
The hydraulic fluid is released through 
an in-line orifice, controlling the 
downward speed and preventing free fall. 
On most machines, additional control 
switches are located at ground level and 
in the cab. 



There are two basic designs of the pow- 
ered safety step. One operates only in 
the "up" and "down" directions. The sec- 
ond design, using a linkage and bearing 
arrangement on the mounting end of the 
lift arms, rotates the step toward the 
machine in conjunction with the lifting 
motion. Thus, the step moves in an arc 
from ground level to platform level. 
Each design is suited for specific appli- 
cations. With minor modifications, a 
powered step can be adapted to any type 
or model of large machinery. 



SUMMARY AND ECONOMIC CONSIDERATIONS 



Evaluation of the safety hazards asso- 
ciated with large mobile mining equipment 
has confirmed that slip and fall acci- 
dents account for a substantial propor- 
tion of vehicle-related accidents. Slips 
and falls while ascending or descending 
equipment constitute over one-third of 
all lost-time accidents associated with 
the operation of haulage trucks, front- 
end loaders , track dozers , shovels , and 
draglines. As a result, the Bureau of 
Mines initiated a program to develop and 
in-mine test improved access systems to 
reduce the hazards associated with mount- 
ing and dismounting large equipment. 

For haulage trucks and front-end load- 
ers , the Bureau of Mines developed a pre- 
tensioned step. The spring steps are de- 
signed to rigidly support the weight of 
the operator as he or she steps up onto 
the equipment, and are highly resistent 
to collision damage because they yield on 
impact if rammed into obstructions such 
as rocks or berms. Because the spring- 
mounted supports are flexible and dur- 
able, the improved ladders can be mounted 
with the bottom step 30 in above the 
ground. 

The improved spring steps can be in- 
stalled on existing haulage trucks or new 
ones at reasonable cost; they cost more 
than the current cable steps, but main- 
tenance and repair costs are substan- 
tially less, with individual replace- 
able parts. The complete step would cost 
around $400 under large-scale production 



and marketing. Although the spring-step 
units are commercially available, the 
Bureau recommends that individual mines 
operators construct their own spring 
steps using the design concepts devel- 
oped in this project. The pre-tensioned 
springs can be purchased in bulk quan- 
tity, and the step unit could be con- 
structed by mine personnel and using 
locally available material. 

In order to reach the cab of track 
dozers , shovels , and draglines , the oper- 
ator must climb up and over the tracks; 
the tracks are usually a part of the pri- 
mary access system. Because of the envi- 
ronment in which the equipment must oper- 
ate, those tracks are usually covered by 
mud, snow, or ice, making them an unsat- 
isfactory accessway. The most hazardous 
area is the zone where the operator 
mounts or dismounts the dozer or shovel. 
The height of the first step is most sig- 
nificant in all cases where the track as- 
sembly must be climbed over. 

Through a cost-sharing agreement, the 
Bureau has helped to develop and test a 
hydraulic lift safety step to transport 
people and supplies from the ground to 
working levels on large surface mining 
equipment. The powered step has proved 
to be a safe, effective method of trans- 
porting operators and material over the 
track assembly. The primary application 
of the powered step is for the large 
track dozers, shovels, and draglines. It 
eliminates hazardous blind steps and 



19 



makes it unnecessary to climb on irregu- 
lar surfaces, such as the track or push 
arm. 

The cost of the powered step ranges 
from $2,000 to $5,000, depending on 
the equipment application. The low- 
maintenance record should justify the in- 
stallation of the powered step, especial- 
ly when compared to the overall cost of 



shovels, draglines, or dozers. Installa- 
tions are recommended for most large doz- 
ers except at mines where the dozer must 
work in close, confining conditions. The 
powered step has proved to be a reliable, 
maintenace-free safety improvement in 
mobile surface mining equipment, and mine 
operators are encouraged to investigate 
the application of this new technology. 



REFERENCES 



1. Gavan, G. A., D. P. Strassel, and 
D. A, Johnson, The Development of Im- 
proved Ingress/Egress Systems for Large 
Haulage Trucks, Pres, at SAE Earthmoving 
Industry Conf. (Peoria, IL, Apr. 14-16, 
1980). SAE Tech. Paper 800680, 1980, 
7 pp. 

2. Gavan, G, A., P, Mote, D. P. Stras- 
sel, and K, Conway. Development and Dem- 
onstration of Improved Truck Ladders 
(contract H0282001, Woodward Associates, 
Inc.). BuMines OFR 87-81, 1979, 332 pp.; 
NTIS PB 81-223406. 

3. Society of Automotive Engineers. 
Access Systems for Off-Road Machines. 
SAE J185, June 1981, 6 pp. 



4, Johnson, D, A. Improved Ingress/ 
Egress Systems For Large Haulage Trucks: 
Development and In-Mine Testing. Paper 
in Surface Mine Truck Safety. Proceed- 
ings: Bureau of Mines Technology Trans- 
fer Seminars, Minneapolis, MN, June 25, 
1980; Birmingham, AL, July 9, 1980; and 
Tucson, AZ, July 24, 1980, Comp. by 
Staff, Bureau of Mines. BuMines IC 8828, 
1980, pp. 40-51. 

5. Winters, K. Analysis of the Pow- 
ered Safety Step Ingress/Egress System 
for the Caterpillar DIG Crawler Tractor 
(contract P3391232, Woodward Associates, 
Inc.). BuMines Final Report, 1979, 65 
pp.; available upon request from D. A. 
Long, BuMines, Minneapolis, MN. 



20 



APPENDIX 

TABLE A-1. - Field test locations for pre-tensioned 
spring step 



Mine 



Operator 



State 



Bingham Canyon 

Bonner Springs Quarry 

Cyprus Pima 

Detroit Salt 

Erie 

Georgetown 

Ribbing Taconite 

Indianhead 

Leahy 

Martiki 

Minntac 

Minorca 

Pinto Valley 

Tilden 

White Pine 



Kennecott 

Lone Star 

AMOCO Minerals.... 
International Salt 
Pickands Mather... 

CONSOL 

Pickands Mather... 
North American. . . . 

AMAX 

MAPCO 

U.S. Steel 

Inland Steel 

Newmont 

Cleveland-Cliffs . . 
Copper Range 



Utah. 

Kansas. 

Arizona. 

Michigan. 

Minnesota. 

Ohio. 

Minnesota. 

North Dakota. 

Illinois. 

Kentucky . 

Minnesota. 

Do. 
Arizona. 
Michigan. 

Do. 



TABLE A-2. - Equipment used for evaluating pre-tensioned spring step 



Equipment 


Manufacturer and model 


Bottom dump coal hauler. ...................... 


Dart 4120, 4150. 


Loader ...•...•.•...............*......•....... 


Caterpillar 988B. 

Michigan 27 5B. 

Caterpillar 777. 

Dart 2085. 

Euclid R-85, R-170. 

Terex 170. 

Unit Rig M36. 

Wabco 120 C, 120 D, 170. 

Caterpillar 657 B. 


Rear dump truck ............................... 


Scraper 





TABLE A-3. - ] 


Field test locations for pow( 


Bred safety step 




Mine 


Operator 


State 


Mine 


Operator 


State 


Ayshire. . . . 
Belle Ayr.. 
Beulah 


AMAX 


Indiana. 
Wyoming . » 
North Dakota. 
Wyoming . 
North Dakota. 
Indiana. 
Wyoming. 


Delta 

Falkirk.... 
Glenharold. 

Hooker 

Indianhead. 
Minnehaha . . 
Seminoe. . . . 


AMAX 


Illinois. 


• ••ClO*«««*»*««* 

Knife River. . . . 
Black Butte.... 
Baukol Noonan. . 
AMAX 


North American. 
CONSOL 


North Dakota. 
Do. 


Black Butte 

Center 

Chinook. ... 


Hooker Chemical 
North American. 
AMAX 


Tennessee. 
North Dakota. 
Indiana. 


Cordero. . . . 


Sunoco 


Arch Mineral. . . 


Wyoming . 



TABLE A-4. - Equipment used for evaluating powered safety step 



Equipment 


Manufacture and model 


Equipment 


Manufacture and model 


Haulage truck 


Unit Rig BD-180. 


Scraper 


Caterpillar 657. 


Dozer 


Caterpillar D7-G, D9-L, 


Shovel 


Bucyrus Erie 155 B, 190 B, 




DIO. 




195 B, 290 B, 295 B. 




Fiat-Allis HD41 B. 




Marion 151 M, 182 M, 




Komatsu D455A-1. 




192 M, 201 M. 


Dragline 


Bucyrus Erie 1570 W. 




P & H 2300. 


Grader 


Caterpillar 16G. 







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